Saturable transformer regulated power system



Nov. 23, 1965 A. RUDAZ SATURABLE TRANSFORMER REGULATED POWER SYSTEM Filed Oct. 17, 1962 2 Sheets-Sheet 1 INVENTOR. ALBI RUDAZ 21, $41M Aw AT TORNEYJ Nov. 23, 1965 A. RUDAZ 3,219,881

SATURABLE TRANSFORMER REGULATED POWER SYSTEM Filed Oct. 17, 1962 2 Sheets-Sheet 2 INVENTOR. ALBI RU DAZ ATTORNEYS United States Patent Ofilice 3,219,881 Patented Nov. 23, 1965 3,219,831 SATURABLE TRANSFORMER REGULATED POWER SYSTEM Albi Rudaz, Geneva, Switzerland, assignor to SA. Des Ateliers de Seeheron, Geneva, Switzerland Filed st. 17, 1962, Ser. No. 231,239

Claims priority, application Switzerland, Dec. 1, 1361,

14,089/61 4 (Ilaims. (it'll. 315-4773) This invention relates to arc welding and, more particularly, to a power supply for alternating current arc welding.

In arc welding, the quality and the appearance of the welded seam depends, other factors being constant, upon the stability of the electric arc. The are stability is primarily related to the ability of the power supply energizing the electrodes to maintain constant current con ditions under changes in arc length and to the wave form of the alternating current in the are.

In many power supplies known to the art, the characteristic curve of output current as a function of output voltage is of such form that any variation of arc length (as, for example, caused by operator movement of the electrode) will change both the voltage across the arc and the arc current. Such current variations, particularly when pronounced, produce concommitant changes in the appearance and quality of the welded seam. The greater the variation of current, the greater the unevenness of the seam because the electrode deposition and fusion rate is proportional to the welding current.

Regulation of the arc current and, thus, are stability is relatively easy to obtain when using direct current and such regulated supplies are known to the art. However, when using an alternating current, current stability is less easily maintained due to the current passage through zero amplitude. Each time the current passes through zero, the arc is extinguished and then reignited due to a transient overvoltage and inherent thermal inertia. Thus, the stability of the arc depends on the slope of the current curve as it passes the zero amplitude.

It is, therefore, the primary object of this invention to provide an alternating power supply for an electric arc, operating at industrial frequencies, in which the current output is regulated and in which the slope of the instantaneous current wave form is steeper than a sinusoidal wave as the current passes through the Zero point.

In accordance with this object, there is provided a power supply having two magnetically independent stages.

Each stage comprises three magnetic cores, a transformer core, a saturable inductance core, and a control or blocking inductance core. A primary transformer winding is wound on each transformer core. A secondary winding is wound on both the transformer and the saturable inductance core. A premagnetization or control winding is wound on both the saturable inductance and the blocking inductance cores.

The stages are electrically interconnected as follows:

The primary transformer windings of each stage are serially connected, series aiding, across the source of alternating voltage at industrial frequencies. The secondary windings are serially connected, series aiding across the arc electrodes, the control windings are serially connected in series opposition across a variable amplitude premagnetization source.

The serially coupled transformer secondary windings step down the source voltage to an open circuit voltage desired for operator safety at the frequency of the source. The output current amplitude is controlled by the saturable inductance core and the current amplitude is stabilized at a desired amplitude despite load variations. The flux in the saturable core is selectably maintained by the premagnetization windings. The control core suppresses circulating induced currents of twice the source frequency, which will result in a current wave form through the secondary windings which has a steep slope as it passes through zero amplitude. Since the control windings are series bucking, the induced voltages of the fundamental and odd numbered harmonics will be cancelled, thus ensuring that control of the output current is related only to control current.

Having briefly described this invention, it will be described in greater detail in the following portions of the specification, which may best be understood by reference to the accompanying drawings, of which:

FIG. 1 is a schematic diagram of power supply constructed in accordance with the present invention;

FIG. 2 is a plot of the R.M.S. values of output voltage as a function of output current, wherein voltage values are plotted along the scale of ordinates and current values are plotted along the scale of abscissa; and

FIG. 3 is a plot of the output current wherein current amplitude is plotted along the scale of ordinates and time is plotted along the scale of abscissa.

In FIG. 1, there is shown a power supply to supply an alternating welding current flowing between a workpiece 10 and welding electrode 12. The power supply comprises two sections or stages 14 and 16 of similar magnetic components. Section 14 comprises a transformer core 18, a saturable inductance core 20 and a control inductance core 22. Similarly, section 18 comprises a transformer core 19, a saturable inductance core 21, and a control inductance core 23; The stages or sections are electrically interconnected by winding couplings.

Primary windings 24, 25 are wound on cores 18 and 19, respectively. The primary windings are serially coupled across an alternating source applied to terminals 26, 28. The alternating voltage source may be a conventional power source of industrial frequencies.

Secondary windings 30, 31 are respectively wound on cores 18 and 2t) and cores 19 and 21. The secondary windings are serially coupled together and between elec' trode 12 and plate 10. Thus, the secondary windings 30 and 31 serve simultaneously as the secondary winding of the step-down transformer energized from the primary windings 24, 25 and serve as the working windings of the saturable core inductances 20, 21.

The saturable cores 2t 21 are premagnetized or preset by the curent flow through windings 32, 33 respectively. Winding 32 is wound on cores 20, 22 and winding 33 is wound on cores 21, 23. Windings 32, 33 are connected in phase opposition and are energized from a rectifying bridge circuit 36 which is energized from an auto transformer 38, coupled to an industrial source of alternating current via terminals 40.

Thus, examining the components, it can be seen that the secondary windings 3t 31 correspond to the secondary of a simple step-down transformer. In this circuit, however, each winding 30 or 31 generates one-half of the total output voltage used for establishment of an arc. The output voltage is, thus, stepped down from the source voltage to that desired for operation and for operator safety under open circuit conditions. However, since the secondary windings are also coupled across cores 2t 21, the output current amplitude may be changed, by change of the premagnetization flux and, thus, the impedance characteristics of the secondary circuit of windings 30, 31. The premagnetization flux is established in cores 20, 21 by the current flow through the windings 32, 33 derived from the bridge circuit 36. Although the bridge supplies a full wave rectified voltage, the impedance of coils 32, 33 will introduce a filtering action and the current through the coils will be direct current or a pulsated direct current.

The cores 20, 211, the secondary windings 3t), 31, and the premagnetization windings 32, 33 respectively wound thereon constitute a series type magnetic amplifier. The amplifier will control the amplitude of the welding current at an adjustable preset amplitude by variation of the setting of the auto transformer 38.

The flow of the working current through the windings 30, 31 will induce a current flow in the premagnetization windings 32, 33 of twice the frequency of the working current. This is a characteristic of series amplifiers. Also, as is known, if the induced currents of twice the working frequency are prevented from circulating in the system, the working current wave form is modified so that the resultant current wave slope is steeper, when passing through zero, than the slope of a sine wave. Since the wave form is symmetrical, it is apparent that the wave form is composed of the addition of the odd harmonics to the basic sinusoidal wave. In order to obtain a steeper slope when passing through zero, the negative maximum of the third harmonic which is the predominant harmonic, must coincide with a positive maximum of the fundamental sine wave.

In the circuitry illustrated, limiting of the circulating current of twice the fundamental frequency is accomplished by the cores 22, 23. The cores are provided with air gaps to ensure that they will not saturate. It should be noted that, if the impedance of the coils 32, 33 could be maintained infinitely high, the current wave form through coils 30, 31 would be a square wave with an infinite slope through zero. The air gap is preferably adjustable to modify the slope of the working current as it passes through zero.

The windings 32, 33 are coupled in phase opposition so as to cancel induced currents of the fundamental or odd harmonic thereof. In this way, control of the premagnetization flux setting is, for practical purposes, entirely dependent only on the premagnetization current in coils 32, 33.

Thus, a stable current are can be maintained despite variation in load, as can be seen from FIG. 2. The plot of the output wave form shown in FIG. 2 illustrates the arc stability, namely, a small change in arc current with a large change in arc voltage.

The output current wave form is shown in FIG. 3. It can be noted from this plot that the slope of the cur- Li rent is increased as it passes the zero point, without change in the frequency from standard industrial frequencies.

This invention may be variously modified and embodied within the scope of the subjoined claims.

What is claimed is:

1. A power supply for alternating current arc welding comprising:

a first and second magnetically independent stage; each of said stages comprising a transformer core, a saturable inductance core, and a control inductance core, a primary transformer winding on each of said transformer cores, a secondary transformer winding on both said transformers and said saturable inductance cores, a control winding on both of said saturable inductance core and said control inductance core;

a source of alternating current, said primary windings in said first and second stages being serially coupled, series aiding, across said source of alternating current;

output welding electrodes, said secondary transformer windings in said first and second stages being serially coupled, series aiding, across said output electrodes; and

a source of unidirectional control current, said control windings being coupled in series opposition across said control current source.

2. A power supply in accordance with claim 1 in which said source of unidirectional control current is adjustable in amplitude.

3. A power supply in accordance with claim 1 in which said control core in each stage is provided with an air gap.

4. A power supply in accordance with claim 1 in which the inductance of the control winding in each stage is high to suppress induced currents of even harmonics of the fundamental frequency in said secondary windings and in which induced currents of the fundamental frequency in each stage are substantially cancelled by electrical coupling of the control windings in phase opposition.

References Qited by the Examiner UNITED STATES PATENTS 2,305,153 12/1942 Fries 323 X 2,322,709 6/1943 Owen 3236l X 2,365,722 12/1944 Owen 323-60 X 2,395,881 3/1946 Klemperer 32356 2,758,162 8/1956 Tekosky 323-56 X LLOYD MCCOLLUM, Primary Examiner. 

1. A POWER SUPPLY FOR ALTERNATING CURRENT ARC WELDING COMPRISING: A FIRST AND SECOND MAGNETICALLY INDEPENDENT STAGE; EACH OF SAID STAGES COMPRISING A TRANSFORMER CORE, A SATURABLE INDUCTANCE CORE, AND A CONTROL INDUCTANCE CORE, A PRIMARY TRANSFORMER WINDING ON EACH OF SAID TRANSFORMER CORES, A SECONDARY TRANSFORMER WINDING ON BOTH SAID TRANSFORMERS AND SAID SATURABLE INDUCTANCE CORES, A CONTROL WINDING ON BOTH OF SAID SATURABLE INDUCTANCE CORE AND SAID CONTROL INDUCTANCE CORE; A SOURCE OF ALTERNATING CURRENT, SAID PRIMARY WINDINGS 